Methods and apparatus for coordination of sending reference signals from multiple cells

ABSTRACT

Methods and apparatus for coordination of sending reference signals in wireless network are disclosed. A network node may select a cell ID based on a measurement of adjacent cells so as to mitigate interference. A network node may communicate information to another network node to control transmitted resources in a protected interval so as to measure channel characteristics.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present Application for Patent is a Divisional application ofapplication Ser. No. 12/818,464, entitled METHOD AND APPARATUS FORCOORDINATION OF SENDING REFERENCE SIGNALS FROM MULTIPLE CELLS, filedJun. 18, 2010 which claims priority to Provisional Application Ser. No.61/219,354, entitled METHODS OF COORDINATION OF SENDING REFERENCESIGNALS FROM MULTIPLE CELLS, filed on Jun. 22, 2009, the content ofwhich is hereby incorporated by reference herein in its entirety for allpurposes.

FIELD

This application is directed generally to wireless communicationssystems. More particularly, but not exclusively, the application relatesto methods and apparatus for coordination of sending reference signalsfrom multiple cells, such as in a long term evolution (LTE) network, aswell as adjusting receivers based on measured interference.

BACKGROUND

Wireless communication systems are widely deployed to provide varioustypes of communication content such as voice, data, video and the like,and deployments are likely to increase with introduction of new dataoriented systems such as Long Term Evolution (LTE) systems. Wirelesscommunications systems may be multiple-access systems capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., bandwidth and transmit power). Examples of suchmultiple-access systems include code division multiple access (CDMA)systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE)systems and other orthogonal frequency division multiple access (OFDMA)systems.

Generally, a wireless multiple-access communication system cansimultaneously support communication for multiple wireless terminals(also know as user equipments (UEs), or access terminals (ATs). Eachterminal communicates with one or more base stations (also know asaccess points (APs), EnodeBs or eNBs) via transmissions on forward andreverse links. The forward link (also referred to as a downlink) refersto the communication link from the base stations to the terminals, andthe reverse link (also referred to as an uplink) refers to thecommunication link from the terminals to the base stations. Thesecommunication links may be established via a single-in-single-out,single-in-multiple out, multiple-in-single-out or amultiple-in-multiple-out (MIMO) system. In MIMO systems, multipleantennas are used in both transmitters and receivers to improvecommunications performance without requiring additional transmit poweror bandwidth. Next generation systems such as Long Term Evolution (LTE)allow for use of MIMO technology for enhanced performance and datathroughput.

As the number of mobile stations deployed increases, the need for properbandwidth utilization becomes more important. Moreover, with theintroduction of semiautonomous base stations for managing small cells,such as femtocells, in systems such as LTE, interference with existingbase stations may become an increasing problem.

SUMMARY

This disclosure relates generally to methods and apparatus forcoordination of sending reference signals from multiple cells, such asin an LTE system.

In one aspect, the disclosure is directed to a method comprisingreceiving transmission coordination information provided by a firstwireless network node and controlling wireless transmission from asecond wireless network node in accordance with the transmissioncoordination information.

In another aspect, the disclosure is directed to a computer programproduct comprising a computer readable medium including codes forcausing a computer to receive transmission coordination informationprovided by a first wireless network node and control wirelesstransmission from a second wireless network node in accordance with thetransmission coordination information.

In another aspect, the disclosure is directed to an apparatus for use ina communication system comprising a coordination module configured toreceive coordination information from a network node and a transmittermodule configured to transmit a signal during a protected intervalresponsive to the coordination information.

In another aspect, the disclosure is directed to a method comprisingreceiving a first reference signal transmitted by a first network node,receiving a second reference signal transmitted by a second network nodeand modifying a functionality of a receiver based upon a relationshipbetween the first reference signal and the second reference signal.

In another aspect, the disclosure is directed to a computer programproduct comprising a computer readable medium including codes forcausing a computer to receive a first reference signal transmitted by afirst network node, receive a second reference signal transmitted by asecond network node, and modify a functionality of a receiver based upona relationship between the first reference signal and the secondreference signal.

In another aspect, the disclosure is directed to an apparatus for use ina communication system comprising a receiver module configured toreceive a first reference signal transmitted by a first network node anda second reference signal transmitted by a second network node, and acontrol module configured to modify a functionality of a receiver basedupon a relationship between the first reference signal and the secondreference signal.

In another aspect, the disclosure is directed to a method comprisingdetermining a time variation in a measurable parameter of one or morereference signals and modifying a functionality of a receiver based uponthe time variation.

In another aspect, the disclosure is directed to a computer programproduct comprising a computer readable medium including codes forcausing a computer to determine a time variation in a measurableparameter of one or more reference signals and modify a functionality ofa receiver based upon the time variation.

In another aspect, the disclosure is directed to an apparatus for use ina communication system comprising a receiver module configured todetermine a time variation in a measurable parameter of one or morereference signals, and a control module configured to modify afunctionality of a receiver based upon the time variation.

In another aspect, the disclosure is directed to a method comprisingdetermining a time variation in an interference level experienced by areceiver, generating a first channel estimate of a wirelesscommunication channel as of a first time, generating a second channelestimate of the wireless communication channel as of a second time,weighting the first channel estimate and the second channel estimate inaccordance with the time variation, thereby generating a first weightedchannel estimate and a second weighted channel estimate, and computing aweighted channel estimate based upon the first weighted channel estimateand the second weighted channel estimate.

In another aspect, the disclosure is directed to a computer programproduct comprising a computer readable medium including codes forcausing a computer to determine a time variation in an interferencelevel experienced by a receiver, generate a first channel estimate of awireless communication channel as of a first time, generate a secondchannel estimate of the wireless communication channel as of a secondtime, weight the first channel estimate and the second channel estimatein accordance with the time variation, thereby generating a firstweighted channel estimate and a second weighted channel estimate, andcompute a weighted channel estimate based upon the first weightedchannel estimate and the second weighted channel estimate.

In another aspect, the disclosure is directed to an apparatus for use ina communication system comprising a receiver module configured toreceive a signal from a wireless communications channel and determine atime variation in an interference level in the channel and a channelestimation module configured to generate a first channel estimate of awireless communication channel as of a first time and a second channelestimate of the wireless communication channel as of a second time,weight the first channel estimate and the second channel estimate inaccordance with the time variation, thereby generating a first weightedchannel estimate and a second weighted channel estimate, and compute aweighted channel estimate based upon the first weighted channel estimateand the second weighted channel estimate.

In another aspect, the disclosure is directed to a method comprisingreceiving a reference signal transmitted by a first network node inaccordance with a first reference signal resource pattern and selecting,for a second network node, a cell identifier associated with a secondreference signal resource pattern different from the first referencesignal resource pattern.

In another aspect, the disclosure is directed to a computer programproduct comprising a computer readable medium including codes forcausing a computer to receive a reference signal transmitted by a firstnetwork node in accordance with a first reference signal resourcepattern and select for a second network node, a cell identifierassociated with a second reference signal resource pattern differentfrom the first reference signal resource pattern.

In another aspect, the disclosure is directed to an apparatus for use ina communication system comprising a receiver module configured toreceive a reference signal transmitted by a first network node inaccordance with a first reference signal resource pattern, and areference signal selector module configured to select a cell identifierassociated with a second reference signal resource pattern differentfrom the first reference signal resource pattern.

Additional aspects are further described below in conjunction with theappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present application may be more fully appreciated in connection withthe following detailed description taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 illustrates details of a wireless communications system includingmultiple cells;

FIG. 2 illustrates details of a wireless communications system;

FIG. 3 is a diagram illustrating elements of a wireless communicationssystem configured for coordination for interference mitigation;

FIG. 4 shows an example process for selecting a cell ID to mitigateinterference in a wireless communications system;

FIG. 5 shows an example process for coordination transmissions tofacilitate channel measurements in a wireless communications system;

FIG. 6 shows an example process for controlling receiver functionalitybased on interference levels;

FIG. 7 shows an example process for receiver adjustment based onsub-frame interference measurement;

FIG. 8 shows a methodology for managing interference in a wirelesscommunication system such as shown in FIG. 1; and

FIG. 9 is an example base station (eNB or HeNB) and associated userterminal (UE) for use in a communication system.

DETAILED DESCRIPTION

This disclosure relates generally to interference coordination andmanagement in wireless communications systems. In various embodiments,the techniques and apparatus described herein may be used for wirelesscommunication networks such as Code Division Multiple Access (CDMA)networks, Time Division Multiple Access (TDMA) networks, FrequencyDivision Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA)networks, Single-Carrier FDMA (SC-FDMA) networks, LTE networks, as wellas other communications networks. As described herein, the terms“networks” and “systems” may be used interchangeably.

In one aspect, the disclosure is directed to a method comprisingreceiving transmission coordination information provided by a firstwireless network node and controlling wireless transmission from asecond wireless network node in accordance with the transmissioncoordination information.

In another aspect, the disclosure is directed to a computer programproduct comprising a computer readable medium including codes forcausing a computer to receive transmission coordination informationprovided by a first wireless network node and control wirelesstransmission from a second wireless network node in accordance with thetransmission coordination information.

In another aspect, the disclosure is directed to an apparatus for use ina communication system comprising a coordination module configured toreceive coordination information from a network node and a transmittermodule configured to transmit a signal during a protected intervalresponsive to the coordination information.

In another aspect, the disclosure is directed to a method comprisingreceiving a first reference signal transmitted by a first network node,receiving a second reference signal transmitted by a second network nodeand modifying a functionality of a receiver based upon a relationshipbetween the first reference signal and the second reference signal.

In another aspect, the disclosure is directed to a computer programproduct comprising a computer readable medium including codes forcausing a computer to receive a first reference signal transmitted by afirst network node, receive a second reference signal transmitted by asecond network node, and modify a functionality of a receiver based upona relationship between the first reference signal and the secondreference signal.

In another aspect, the disclosure is directed to an apparatus for use ina communication system comprising a receiver module configured toreceive a first reference signal transmitted by a first network node anda second reference signal transmitted by a second network node, and acontrol module configured to modify a functionality of a receiver basedupon a relationship between the first reference signal and the secondreference signal.

In another aspect, the disclosure is directed to a method comprisingdetermining a time variation in a measurable parameter of one or morereference signals and modifying a functionality of a receiver based uponthe time variation.

In another aspect, the disclosure is directed to a computer programproduct comprising a computer readable medium including codes forcausing a computer to determine a time variation in a measurableparameter of one or more reference signals and modify a functionality ofa receiver based upon the time variation.

In another aspect, the disclosure is directed to an apparatus for use ina communication system comprising a receiver module configured todetermine a time variation in a measurable parameter of one or morereference signals, and a control module configured to modify afunctionality of a receiver based upon the time variation.

In another aspect, the disclosure is directed to a method comprisingdetermining a time variation in an interference level experienced by areceiver, generating a first channel estimate of a wirelesscommunication channel as of a first time, generating a second channelestimate of the wireless communication channel as of a second time,weighting the first channel estimate and the second channel estimate inaccordance with the time variation, thereby generating a first weightedchannel estimate and a second weighted channel estimate, and computing aweighted channel estimate based upon the first weighted channel estimateand the second weighted channel estimate.

In another aspect, the disclosure is directed to a computer programproduct comprising a computer readable medium including codes forcausing a computer to determine a time variation in an interferencelevel experienced by a receiver, generate a first channel estimate of awireless communication channel as of a first time, generate a secondchannel estimate of the wireless communication channel as of a secondtime, weight the first channel estimate and the second channel estimatein accordance with the time variation, thereby generating a firstweighted channel estimate and a second weighted channel estimate, andcompute a weighted channel estimate based upon the first weightedchannel estimate and the second weighted channel estimate.

In another aspect, the disclosure is directed to an apparatus for use ina communication system comprising a receiver module configured toreceive a signal from a wireless communications channel and determine atime variation in an interference level in the channel and a channelestimation module configured to generate a first channel estimate of awireless communication channel as of a first time and a second channelestimate of the wireless communication channel as of a second time,weight the first channel estimate and the second channel estimate inaccordance with the time variation, thereby generating a first weightedchannel estimate and a second weighted channel estimate, and compute aweighted channel estimate based upon the first weighted channel estimateand the second weighted channel estimate.

In another aspect, the disclosure is directed to a method comprisingreceiving a reference signal transmitted by a first network node inaccordance with a first reference signal resource pattern and selecting,for a second network node, a cell identifier associated with a secondreference signal resource pattern different from the first referencesignal resource pattern.

In another aspect, the disclosure is directed to a computer programproduct comprising a computer readable medium including codes forcausing a computer to receive a reference signal transmitted by a firstnetwork node in accordance with a first reference signal resourcepattern and select for a second network node, a cell identifierassociated with a second reference signal resource pattern differentfrom the first reference signal resource pattern.

In another aspect, the disclosure is directed to an apparatus for use ina communication system comprising a receiver module configured toreceive a reference signal transmitted by a first network node inaccordance with a first reference signal resource pattern, and areference signal selector module configured to select a cell identifierassociated with a second reference signal resource pattern differentfrom the first reference signal resource pattern.

Various other aspects and features of the disclosure are furtherdescribed below. It should be apparent that the teachings herein may beembodied in a wide variety of forms and that any specific structure,function, or both being disclosed herein is merely representative. Basedon the teachings herein one skilled in the art should appreciate that anaspect disclosed herein may be implemented independently of any otheraspects and that two or more of these aspects may be combined in variousways. For example, an apparatus may be implemented or a method may bepracticed using any number of the aspects set forth herein. In addition,such an apparatus may be implemented or such a method may be practicedusing other structure, functionality, or structure and functionality inaddition to or other than one or more of the aspects set forth herein.Furthermore, an aspect may comprise at least one element of a claim.

A CDMA network may implement a radio technology such as UniversalTerrestrial Radio Access (UTRA), cdma2000 and the like. UTRA includesWideband-CDMA (W-CDMA) and Low Chip Rate (LCR). Cdma2000 covers IS-2000,IS-95 and IS-856 standards. A TDMA network may implement a radiotechnology such as Global System for Mobile Communications (GSM).

An OFDMA network may implement a radio technology such as Evolved UTRA(E-UTRA), IEEE 802.11, IEEE 802.16, IEEE 802.20, Flash-OFDM and thelike. UTRA, E-UTRA, and GSM are part of Universal MobileTelecommunication System (UMTS). In particular, Long Term Evolution(LTE) is a release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS andLTE are described in documents provided from an organization named “3rdGeneration Partnership Project” (3GPP), and cdma2000 is described indocuments from an organization named “3rd Generation Partnership Project2” (3GPP2). These various radio technologies and standards are known orare being developed in the art. For example, the 3rd GenerationPartnership Project (3GPP) is a collaboration between groups oftelecommunications associations that aims to define a globallyapplicable third generation (3G) mobile phone specification. 3GPP LongTerm Evolution (LTE) is a 3GPP project aimed at improving the UniversalMobile Telecommunications System (UMTS) mobile phone standard. The 3GPPmay define specifications for the next generation of mobile networks,mobile systems, and mobile devices. For clarity, certain aspects of theapparatus and techniques are described below for LTE implementations,and LTE terminology is used in much of the description below; however,the description is not intended to be limited to LTE applications.Accordingly, it will be apparent to one of skill in the art that theapparatus and methods described herein may be applied to various othercommunications systems and applications.

Logical channels in wireless communications systems may be classifiedinto Control Channels and Traffic Channels. Logical Control Channels maycomprise a Broadcast Control Channel (BCCH) which is a downlink (DL)channel for broadcasting system control information, a Paging ControlChannel (PCCH) which is a DL channel that transfers paging informationand a Multicast Control Channel (MCCH) which is a point-to-multipoint DLchannel used for transmitting Multimedia Broadcast and Multicast Service(MBMS) scheduling and control information for one or several MTCHs.Generally, after establishing a Radio Resource Control (RRC) connectionthis channel is only used by UEs that receive MBMS. A Dedicated ControlChannel (DCCH) is a point-to-point bi-directional channel that transmitsdedicated control information and is used by UEs having an RRCconnection.

Logical Traffic Channels may comprise a Dedicated Traffic Channel (DTCH)which is point-to-point bi-directional channel, dedicated to one UE, forthe transfer of user information, and a Multicast Traffic Channel (MTCH)for Point-to-multipoint DL channel for transmitting traffic data.

Transport Channels may be classified into downlink (DL) and uplink (UL)Transport Channels. DL Transport Channels may comprise a BroadcastChannel (BCH), Downlink Shared Data Channel (DL-SDCH) and a PagingChannel (PCH). The PCH may be used for support of UE power saving (whena DRX cycle is indicated by the network to the UE), broadcast over anentire cell and mapped to Physical Layer (PHY) resources which can beused for other control/traffic channels. The UL Transport Channels maycomprise a Random Access Channel (RACH), a Request Channel (REQCH), anUplink Shared Data Channel (UL-SDCH) and a plurality of PHY channels.The PHY channels may comprise a set of DL channels and UL channels.

In addition, the DL PHY channels may comprise the following:

Common Pilot Channel (CPICH)

Synchronization Channel (SCH)

Common Control Channel (CCCH)

Shared DL Control Channel (SDCCH)

Multicast Control Channel (MCCH)

Shared UL Assignment Channel (SUACH)

Acknowledgement Channel (ACKCH)

DL Physical Shared Data Channel (DL-PSDCH)

UL Power Control Channel (UPCCH)

Paging Indicator Channel (PICH)

Load Indicator Channel (LICH)

The UL PHY Channels may comprise the following:

Physical Random Access Channel (PRACH)

Channel Quality Indicator Channel (CQICH)

Acknowledgement Channel (ACKCH)

Antenna Subset Indicator Channel (ASICH)

Shared Request Channel (SREQCH)

UL Physical Shared Data Channel (UL-PSDCH)

Broadband Pilot Channel (BPICH)

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any aspect and/or embodiment describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other aspects and/or embodiments.

For purposes of explanation of various aspects and/or embodiments, thefollowing terminology and abbreviations may be used herein:

AM Acknowledged Mode

AMD Acknowledged Mode Data

ARQ Automatic Repeat Request

BCCH Broadcast Control CHannel

BCH Broadcast CHannel

C- Control-

CCCH Common Control CHannel

CCH Control CHannel

CCTrCH Coded Composite Transport Channel

CP Cyclic Prefix

CRC Cyclic Redundancy Check

CTCH Common Traffic CHannel

DCCH Dedicated Control CHannel

DCH Dedicated CHannel

DL DownLink

DSCH Downlink Shared CHannel

DTCH Dedicated Traffic CHannel

FACH Forward link Access CHannel

FDD Frequency Division Duplex

L1 Layer 1 (physical layer)

L2 Layer 2 (data link layer)

L3 Layer 3 (network layer)

LI Length Indicator

LSB Least Significant Bit

MAC Medium Access Control

MBMS Multmedia Broadcast Multicast Service

MCCH MBMS point-to-multipoint Control CHannel

MRW Move Receiving Window

MSB Most Significant Bit

MSCH MBMS point-to-multipoint Scheduling CHannel

MTCH MBMS point-to-multipoint Traffic CHannel

PCCH Paging Control CHannel

PCH Paging CHannel

PDU Protocol Data Unit

PHY PHYsical layer

PhyCH Physical CHannels

RACH Random Access CHannel

RLC Radio Link Control

RRC Radio Resource Control

SAP Service Access Point

SDU Service Data Unit

SHCCH SHared channel Control CHannel

SN Sequence Number

SUFI SUper FIeld

TCH Traffic CHannel

TDD Time Division Duplex

TFI Transport Format Indicator

TM Transparent Mode

TMD Transparent Mode Data

TTI Transmission Time Interval

U- User-

UE User Equipment

UL UpLink

UM Unacknowledged Mode

UMD Unacknowledged Mode Data

UMTS Universal Mobile Telecommunications System

UTRA UMTS Terrestrial Radio Access

UTRAN UMTS Terrestrial Radio Access Network

MBSFN Multicast broadcast single frequency network

MCE MBMS coordinating entity

MCH Multicast channel

DL-SCH Downlink shared channel

MSCH MBMS control channel

PDCCH Physical downlink control channel

PDSCH Physical downlink shared channel

A MIMO system employs multiple (N_(T)) transmit antennas and multiple(N_(R)) receive antennas for data transmission. A MIMO channel formed bythe N_(T) transmit and N_(R) receive antennas may be decomposed intoN_(S) independent channels, which are also referred to as spatialchannels. The maximum spatial multiplexing N_(S) if a linear receiver isused is min(N_(T), N_(R)), with each of the N_(S) independent channelscorresponding to a dimension. This provides an N_(S) increase inspectral efficiency. A MIMO system can provide improved performance(e.g., higher throughput and/or greater reliability) if the additionaldimensionalities created by the multiple transmit and receive antennasare utilized. The special dimension may be described in terms of a rank.

MIMO systems support time division duplex (TDD) and frequency divisionduplex (FDD) implementations. In a TDD system, the forward and reverselink transmissions use the same frequency regions so that thereciprocity principle allows the estimation of the forward link channelfrom the reverse link channel. This enables the access point to extracttransmit beamforming gain on the forward link when multiple antennas areavailable at the access point.

System designs may support various time-frequency reference signals forthe downlink and uplink to facilitate beamforming and other functions. Areference signal is a signal generated based on known data and may alsobe referred to as a pilot, preamble, training signal, sounding signaland the like. A reference signal may be used by a receiver for variouspurposes such as channel estimation, coherent demodulation, channelquality measurement, signal strength measurement and the like. MIMOsystems using multiple antennas generally provide for coordination ofsending of reference signals between antennas, however, LTE systems donot in general provide for coordination of sending of reference signalsfrom multiple base stations or eNBs.

3GPP Specification 36211-900 defines in Section 5.5 particular referencesignals for demodulation, associated with transmission of PUSCH orPUCCH, as well as sounding, which is not associated with transmission ofPUSCH or PUCCH. For example, Table 1 lists some reference signals forLTE implementations that may be transmitted on the downlink and uplinkand provides a short description for each reference signal. Acell-specific reference signal may also be referred to as a commonpilot, a broadband pilot and the like. A UE-specific reference signalmay also be referred to as a dedicated reference signal.

TABLE 1 Link Reference Signal Description Downlink Cell SpecificReference signal sent by a Node B Reference Signal and used by the UEsfor channel estimation and channel quality measurement. Downlink UESpecific Reference signal sent by a Node B Reference Signal to aspecific UE and used for demodulation of a downlink transmission fromthe Node B. Uplink Sounding Reference signal sent by a UE and ReferenceSignal used by a Node B for channel estimation and channel qualitymeasurement. Uplink Demodulation Reference signal sent by a UE andReference Signal used by a Node B for demodulation of an uplinktransmission from the UE.

In some implementations a system may utilize time division duplexing(TDD). For TDD, the downlink and uplink share the same frequencyspectrum or channel, and downlink and uplink transmissions are sent onthe same frequency spectrum. The downlink channel response may thus becorrelated with the uplink channel response. A reciprocity principle mayallow a downlink channel to be estimated based on transmissions sent viathe uplink. These uplink transmissions may be reference signals oruplink control channels (which may be used as reference symbols afterdemodulation). The uplink transmissions may allow for estimation of aspace-selective channel via multiple antennas.

In LTE implementations orthogonal frequency division multiplexing isused for the downlink—that is, from the base station, access point oreNodeB to the terminal or UE. Use of OFDM meets the LTE requirement forspectrum flexibility and enables cost-efficient solutions for very widecarriers with high peak rates, and is a well-established technology, forexample OFDM is used in standards such as IEEE 802.11a/g, 802.16,HIPERLAN-2, DVB and DAB.

Time frequency physical resource blocks (also denoted here in asresource blocks or “RBs” for brevity) may be defined in OFDM systems asgroups of transport carriers (e.g. sub-carriers) or intervals that areassigned to transport data. The RBs are defined over a time andfrequency period. Resource blocks are comprised of time-frequencyresource elements (also denoted here in as resource elements or “REs”for brevity), which may be defined by indices of time and frequency in aslot. Additional details of LTE RBs and REs are described in 3GPP TS36.211.

UMTS LTE supports scalable carrier bandwidths from 20 MHz down to 1.4MHZ. In LTE, an RB is defined as 12 sub-carriers when the sub-carrierbandwidth is 15 kHz, or 24 sub-carriers when the sub-carrier bandwidthis 7.5 kHz. In an exemplary implementation, in the time domain there isa defined radio frame that is 10 ms long and consists of 10 sub framesof 1 ms each. Every sub frame consists of 2 slots, where each slot is0.5 ms. The subcarrier spacing in the frequency domain in this case is15 kHz. +Twelve of these subcarriers together (per slot) constitutes anRB, so in this implementation one resource block is 180 kHz. 6 Resourceblocks fit in a carrier of 1.4 MHz and 100 resource blocks fit in acarrier of 20 MHz.

In the downlink there are typically a number of physical channels asdescribed above. In particular, the PDCCH is used for sending control,the PHICH for sending ACK/NACK, the PCFICH for specifying the number ofcontrol symbols, the Physical Downlink Shared Channel (PDSCH) for datatransmission, the Physical Multicast Channel (PMCH) for broadcasttransmission using a Single Frequency Network, and the PhysicalBroadcast Channel (PBCH) for sending important system information withina cell. Supported modulation formats on the PDSCH in LTE are QPSK, 16QAMand 64QAM.

In the uplink there are typically three physical channels. While thePhysical Random Access Channel (PRACH) is only used for initial accessand when the UE is not uplink synchronized, the data is sent on thePhysical Uplink Shared Channel (PUSCH). If there is no data to betransmitted on the uplink for a UE, control information would betransmitted on the Physical Uplink Control Channel (PUCCH). Supportedmodulation formats on the uplink data channel are QPSK, 16QAM and 64QAM.

If virtual MIMO/spatial division multiple access (SDMA) is introducedthe data rate in the uplink direction can be increased depending on thenumber of antennas at the base station. With this technology more thanone mobile can reuse the same resources. For MIMO operation, adistinction is made between single user MIMO, for enhancing one user'sdata throughput, and multi user MIMO for enhancing the cell throughput.

In 3GPP LTE, a mobile station or device may be referred to as a “userdevice” or “user equipment” (UE). A base station may be referred to asan evolved NodeB or eNB. A semi-autonomous base station may be referredto as a home eNB or HeNB. An HeNB may thus be one example of an eNB. TheHeNB and/or the coverage area of an HeNB may be referred to as afemtocell, an HeNB cell or a closed subscriber group (CSG) cell (whereaccess is restricted).

Attention is now directed to FIG. 1, which shows a wirelesscommunication system 100 with multiple user equipments (UEs) 104, a homeevolved NodeB (HeNB) 110, two evolved NodeBs (eNB) 102, 132, a relaynode 106, and a core or backhaul network 108. The eNB 102 may be thecentral base station in a wireless communication system. The eNB 132 maybe an eNB in an adjacent macrocell (denoted as Macro Cell 2), and may beassociated with components such as those shown in FIG. 1 incommunication with Macro Cell 1 (components are omitted from FIG. 1 forclarity). A UE 104 may also be called, and may contain some or all ofthe functionality of, a terminal, a mobile station, an access terminal,a subscriber unit, a station, etc. A UE 104 may be a cellular phone, apersonal digital assistant (PDA), a wireless device, a wireless modem, ahandheld device, a laptop computer, etc.

The core network 108 may be the central piece of a telecommunicationsnetwork. For example, the core network 108 may facilitate communicationswith the Internet, other UEs, etc. A UE 104 may communicate with thecore network 108 through an eNB 102, 132 or an HeNB 110. Multiple UEs104 may be in wireless communication with an eNB 102 or an HeNB 110.eNBs 102 and 132, and HeNB 110 may communicate with the core networkand/or to each other either directly or through the core network 108.

The term “eNB” may be used to refer to the eNB 102 or to the HeNB 110,because the HeNB 110 may be considered to be one type of eNB. The eNB102 may be referred to as a macro-eNB 102 or macrocell eNB 102. Amacro-eNB 102 may have a much larger range than an HeNB 110.Furthermore, a macro-eNB 102 may provide unrestricted access to UEs 104a subscribing to the core network 108 (i.e., in a non-CSGconfiguration). In contrast, an HeNB 110 may provide restricted accessto UEs 104 b belonging to a closed subscriber group (CSG). It may beassumed that a UE 104 may only communicate with a single eNB at a giventime. Thus, a UE 104 b communicating with an HeNB 110 may not generallysimultaneously communicate with a macro-eNB 102, however, somecommunication may be performed to facilitate UE management, inter-cellcoordination, etc. This will generally include transfer of controlinformation but not data.

The coverage area of an eNB may be referred to as a cell. Depending onsectoring, one or more cells may be served by the eNB. The coverage areaof a macroeNB 102 may be referred to as a macrocell 112 or an eNB cell(shown as Macro Cell 1 in FIG. 1). Likewise, the coverage area of anHeNB 110 may be referred to as an HeNB-cell 114 or a femtocell. As shownin FIG. 1, multiple cells may be adjacent to and/or overlapping. Forexample, in FIG. 1, Macro Cells 1 and 2 overlap femtocell 114.Obviously, many other variations of adjacent and/or overlapping cellsare possible in various system implementations.

Multiple eNBs may have a backhaul connection with each other through thecore network 108. For example, a backhaul connection may exist betweenthe HeNB 110 and eNBs 102 and 132. In a backhaul connection, an eNB maycommunicate with the core network 108 and the core network 108 maycorrespondingly communicate with the HeNB 110. A direct connection mayalso exist between multiple eNBs.

For example, a direct connection may exist between the HeNB 110 and theeNB 102. The direct connection may be an X2 connection 120. Detailsabout an X2 interface may be found in, for example, 3GPP TS 36.423×2-AP.Multiple eNBs may also have a connection 122, 124 through use of a relaynode 106. In one configuration, the relay node 106 may be the corenetwork 108.

The coverage range for a macrocell 112 may be much larger than thecoverage range for an HeNB-cell 114. In one configuration, the coveragerange for a macrocell 112 may include the entire coverage range for anHeNB-cell 114.

A UE 104 may communicate with a base station (e.g., the eNB 102 or theHeNB 110) via transmissions on an uplink 116 and a downlink 118. Theuplink 116 (or reverse link) refers to the communication link from theUE 104 to a base station, and the downlink 118 (or forward link) refersto the communication link from the base station to the UE 104. Thus, aUE 104 a may communicate with the eNB 102 via the uplink 116 a anddownlink 118 a. Likewise, a UE 104 b may communicate with the HeNB 110via the uplink 116 b and downlink 118 b.

The resources of the wireless communication system 100 (e.g., bandwidthand transmit power) may be shared among multiple UEs 104. A variety ofmultiple access techniques are known, including code division multipleaccess (CDMA), time division multiple access (TDMA), frequency divisionmultiple access (FDMA), orthogonal frequency division multiple access(OFDMA), single-carrier frequency division multiple access (SC-FDMA),and so forth.

In some configurations, one or more macro-UEs 104 a located within anHeNB-cell 114 may cause interference so as to interfere with or jam theHeNB-cell 114. For example, a macro-UE 104 a located within an HeNB-cell114 may cause interference for communications between an HeNB-UE 104 band the HeNB 110. Likewise, a macro-UE 104 a within the HeNB-cell 114may not have macrocell 112 coverage due to interference from other HeNBsor eNBs. Both uplink interference 130 and downlink interference 132 mayoccur.

If there are no UEs 104 in the CSG cell (e.g., HeNB cell 114), there maybe no interference issues. In order to allow a successful initial accessby a UE 104 to the CSG cell, the CSG cell may dynamically bias the openloop power control algorithm to balance the effect of high interference.CSG cells may also add noise to balance the uplink 116 and the downlink118.

Inter-cell interference coordination (ICIC) may be used to prevent theuplink interference 130 and/or the downlink interference 132. FrequencyICIC may be feasible for both synchronous and asynchronous deployments.Time ICIC may be feasible in synchronized deployments. Inter-cellinterference coordination and mitigation may be facilitated bycoordination and control of transmissions between combinations of eNBsand HeNBs, by self-selection of cell ID, and/or by interferencemonitoring and receiver adjustment.

In one aspect, interference management may be facilitated by determininginformation associated with a cell node at the UE and supplying theinformation to the node (eNB or HeNB). The information may includespatial channel information, power level information, or otherinformation associated with the femtocell or femtocell node. Forexample, the UE may determine Reference Signal Received Power (RSRP),which for a particular cell may be the average power measured (and theaverage between receiver branches) of the resource elements that containcell specific reference signals. The UE may also determine ReferenceSignal Received Quality (RSRQ) as the ratio of the RSRP and the E-UTRACarrier Received Signal Strength Indicator (RSSI), for the referencesignals. The UE may also determine other signal metrics. For example,the UE may determine power used (power contribution) for the resourceelements that are used to transmit cell-specific reference signals froman eNB or HeNB (in the system bandwidth). The UE may also determine aChannel Quality Indicator (CQI), a Rank Indicator (RI), and a PrecodingMatrix Indicator (PMI). The CQI provides information to the eNB or HeNBabout the link adaptation parameters the UE can support at the time. TheCQI is a table containing modulation and coding information. The RI is aUE recommendation for the number of layers, i.e., streams, to be used inspatial multiplexing. The UE may also determine received interferencepower per physical resource block, as well as thermal noise power overthe system bandwidth.

Spatial channel information may be determined and composed in ameasurement report to be sent to an eNB or HeNB. The spatial informationand/or power information may then be used by the node to coordinatetransmissions from other nodes so as to mitigate interference with theUE. Information may be communicated directl between eNBs and/or HeNBs ormay be relayed using backhaul signaling.

In various implementations, power determination of the adjacent channelmay be based on particular components or subcarriers of the adjacentchannel signal, which may correspondingly be based on the adjacentnetwork type. For example, the received power may be determined based ona particular subcarrier or signal in the adjacent channel, such as apilot signal, with the determined power based on a measurement of thepilot signal. The pilot signal may be a pilot signal in a dedicated orallocated pilot sub-channel of the adjacent channel. For example,reference signals, as are defined with respect to LTE, may be used as apilot signal and processed to determine power level. In UTRAimplementations, alternate pilot signals are used and these may be usedto determine adjacent network power metrics and levels. Channelcharacteristics, such as fading characteristics, may be determinedthrough use of reference signals and may be reported to eNBs or HeNBs.

In some implementations, an average or peak power level measurement maybe made on the adjacent channel signal. This may be, for example, apower density determination made on the adjacent channel signal. Otherpower determinations may also be used and/or combined with thosedescribed above. For example, in one implementation, a power densitymeasurement may be combined with a peak determination or pilot signaldetermination to generate a power level metric.

In some implementations, the received signal power level metric may bebased on a Reference Signal Received Power (RSRP) per resource element,with the determining including determining the Reference Signal ReceivedPower per resource element by measuring, at the node, a Reference Signaltransmitted on one of the adjacent channels. In addition, the RSRP maybe based on the average of RSRP per resource element across multipletransmit antennas, such as in a MIMO system.

FIG. 2 illustrates a wireless communication system 200 with a macro-eNB202 and multiple HeNBs 210. The wireless communication system 200 mayinclude an HeNB gateway 234 for scalability reasons. The macro-eNB 202and the HeNB gateway 234 may each communicate with a pool 240 ofmobility management entities (MME) 242 and a pool 244 of servinggateways (SGW) 246. The HeNB gateway 234 may appear as a C-plane and aU-plane relay for dedicated S1 connections 236. An S1 connection 236 maybe a logical interface specified as the boundary between an evolvedpacket core (EPC) and an Evolved Universal Terrestrial Access Network(EUTRAN). The HeNB gateway 234 may act as a macro-eNB 202 from an EPCpoint of view. The C-plane interface may be S1-MME and the U-planeinterface may be S1-U.

The HeNB gateway 234 may act towards an HeNB 210 as a single EPC node.The HeNB gateway 234 may ensure S1-flex connectivity for an HeNB 210.The HeNB gateway 234 may provide a 1:n relay functionality such that asingle HeNB 210 may communicate with n MMEs 242. The HeNB gateway 234registers towards the pool 240 of MMEs 242 when put into operation viathe S1 setup procedure. The HeNB gateway 234 may support setup of S1interfaces 236 with the HeNBs 210.

The wireless communication system 200 may also include a self organizingnetwork (SON) server 238. The SON server 238 may provide automatedoptimization of a 3GPP LTE network. The SON server 238 may be a keydriver for improving operation and maintenance (O&M) to the wirelesscommunication system 200. An X2 link 220 may exist between the macro-eNB202 and the HeNB gateway 234. X2 links 220 may also exist between eachof the HeNBs 210 connected to a common HeNB gateway 234. The X2 links220 may be set up based on input from the SON server 238. An X2 link 220may convey ICIC information. If an X2 link 220 cannot be established,the S1 link 236 may be used to convey ICIC information. Backhaulsignaling may be used in communication system 200 to manage interferencemitigation between macro-eNB 202 and HeNBs 210.

Attention is now directed to FIG. 3, which illustrates an embodiment ofa network 300 employing coordination components configured to mitigateinterference across a wireless network 310.

It is noted that the system 300 can be employed with an access terminalor mobile device, and can be, for instance, a module such as an SD card,a network card, a wireless network card, a computer (including laptops,desktops, personal digital assistants (PDAs)), mobile phones, smartphones, or any other suitable terminal that can be utilized to access anetwork. The terminal accesses the network by way of an access component(not shown). In one example, a connection between the terminal and theaccess components may be wireless in nature, in which access componentsmay be the base station and the mobile device is a wireless terminal.For instance, the terminal and base stations may communicate by way ofany suitable wireless protocol, including but not limited to TimeDivisional Multiple Access (TDMA), Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Orthogonal Frequency DivisionMultiplexing (OFDM), FLASH OFDM, Orthogonal Frequency Division MultipleAccess (OFDMA), or any other suitable protocol.

Access components can be an access node associated with a wired networkor a wireless network. To that end, access components can be, forinstance, a router, a switch, or the like. The access component caninclude one or more interfaces, e.g., communication modules, forcommunicating with other network nodes. Additionally, the accesscomponent can be a base station (or wireless access point) in a cellulartype network, wherein base stations (or wireless access points) areutilized to provide wireless coverage areas to a plurality ofsubscribers. Such base stations (or wireless access points) can bearranged to provide contiguous areas of coverage to one or more cellularphones and/or other wireless terminals.

System 300 may correspond to the wireless networks shown in FIGS. 1 and2. System 300 may include one or more base stations 320 (also referredto as a node, evolvedNode B—eNB, serving eNB, target eNB, femto station,pico station and the like) which can be an entity capable ofcommunication over the wireless network 310 to various devices 330. Forinstance, each device 330 can be an access terminal (also referred to asterminal, user equipment (UE), mobility management entity (MME) ormobile device) or in some cases may be an eNB or HeNB. For purposes ofbrevity, the device 330 will be referred to here in as a UE and the basestation 320 will be referred to herein as an eNB or HeNB. The eNB 320and UE 330 may include coordination components 340 and 344 respectively,which may comprise hardware, software, firmware or combinations of theseelements in various embodiments. It is to be appreciated thatcoordination to mitigate interference may occur between base stations,between base stations and devices, and/or between base stations,devices, and other network components such as a network manager orserver. Coordination may include communicative connections betweenmobile devices and base stations, base stations and base stations, ormobile devices and mobile devices. Communications may be via wirelesslinks or may be via wired connections such as backhaul connections.

As shown, the eNB 320 may communicate to the UE 330 (or UEs 330) viadownlink 360 and may receive data via uplink 370. Such designation asuplink and downlink is arbitrary as the UE 330 can also transmit datavia downlink and receive data via uplink channels. It is noted thatalthough two network components 320 and 330 are shown, that more thantwo components can be employed on the network 310 in variousconfigurations, with such additional components also being adapted forreference signal coordination as described herein.

In general, when the UE 330 cannot connect a desired cell with thestrongest downlink channel, it may see strong interference in variousdownlink scenarios or applications. The strongest downlink channel isgenerally the one with the strongest reference signals. When a UE cannotconnect to a desired cell with the strongest downlink channel (forexample, a UE in proximity to a restricted HeNB, such UE 104 inproximity to HeNB 110 as shown in FIG. 1), or where the downlink may begood but the uplink is not, the UE may benefit from interferencemitigation.

For systems deploying with varying transmitting power and/or withrestricted association, or where the eNB 330 tries to balance loading byoffloading some users from one cell to a different cell, such as betweenmacrocells 1 and 2 as shown in FIG. 1, the UE may use interferencecancellation or other advanced receivers to improve the receiverperformance. Channel estimates are important for those advancedreceivers. Channel estimation may be facilitated in systems such as LTEsystems through use of reference signals, which may be arranged inresource blocks so as to allow a receiver to determine channelcharacteristics such as fading, power levels and the like by measuringand processing the received reference signals.

Consequently, it is desirable that the reference signal does not seestrong interference, which may come from other components of a networksuch as are shown in FIG. 1, including other eNBs and/or HeNBs.Accordingly, in self organizing network configurations (SONs), wheredeployment of HeNBs may be done in a relatively uncontrolled fashionand/or may vary over time, the eNB (or HeNB) 320 may choose a cellidentity to prevent cell ID collision with other cells such as othermacro, pico, and/or femtocells, for example. Alternately, or inaddition, further cell ID selection criteria may be enforced such thatat least the reference signal will not see strong interference (forexample, by halting data or control information transmission duringtime-frequency resources allocated to the reference signals).

Generally, reference signal resource mappings in the frequency domainare linked to the cell ID, where different cell IDs may have differentfrequency shifts. There are limited number of frequency locations thatcan be reused for reference signal. In some implementations an eNB orHeNB may search and find a suitable cell ID for itself. For example, thenodes may be part of a self organizing network (SON), e.g., where afemto cell may search for a suitable cell ID before configuring itsrespective cell ID. In an exemplary embodiment, the cell ID is selectedso that the associated reference signals are orthogonal to anothercell's reference signals. This may be done based on the shifts asdefined in LTE, where in a 1 antenna MIMO system there are 6 availableshifts, and in a 2 antenna system there are 3 available shifts.

Accordingly, system 300 may be configured to mitigate interference inwireless communications networks 310. In one aspect, if a base stationsuch as an HeNB or eNB locates a strong adjacent cell, the eNB or HeNBcan select a cell ID such that the associated reference signal isselected to mitigate interference with other known cells/referencesignal patterns. For example, a reference signal may be selected so thatits signal mappings are orthogonal to this strong cell, such as where areference signal occupies different frequency resources used by anon-CSG cell. Different cell IDs may have different frequency shifts,however, there are a limited number of frequency locations that can bereused for reference signals.

Initial cell ID selection and assignment may be done in different ways.For example, there may be a reserved set of cell IDs assigned forfemtocells (and associated HeNBs). When a new HeNB is powered up, it mayinitially listen to determine whether there are adjacent macrocellsand/or or cells such as femtocells. Based on this information, one ofthe reserved cell IDs may be assigned to the new HeNB. However, if thisinitial cell ID corresponds with reference signals that causeinterference with adjacent cells, the initial cell ID may subsequentlybe changed so as to address interference issues, such as is furtherdescribed below.

In some cases, an eNB may decide to apply the strategy above based onthe type of a cell which causes strong interference, e.g., whether thecell is a closed subscriber group (CSG) cell or non-CSG cell. A CSG cellgenerally has a limited number of allowable subscribers. Although a UEthat is not associated with the CSG cell may be able to communicate in alimited fashion with the CSG cell, it may not be able to send or receivedata. Femtocells may be CSG or non-CSG. A so-called open femtocell maybe controlled by a carrier and may allow open access to any subscriber.Other femtocells may be CSG, which only certain users may access.

For example, an HeNB (or in some implementations an eNB or other basestation) may initially listen to determine which other cells areadjacent, and may then select a cell ID based on the determination ofcell ID/reference signals used and/or the type of cell (HeNBs have UElistening functionality). An HeNB may select or be assigned a particularcell ID if interference originates from a CSG cell, however, it maychoose not to do so if the interference originates from a non-CSG cell.This selection may be based on a table or other information stored in amemory or other data storage device in the HeNB. For example, the HeNBmay include a table or algorithm to determine optimal orthogonalreference signals/cell IDs based on other cells it detects at initiationand their associated cell IDs/reference signal patterns. The optimalreference signal may be selected based on the particularly identifiedadjacent cell IDs/reference signals, cell type and/or may also be basedon other parameters such as power levels/signal strength of the adjacentcell nodes, or other parameters. In some implementations, the cell IDmay be selected based on communications with a core network and/or MME,such as are shown in FIGS. 1 and 2, which may manage cell ID assignment.In some implementations, the cell ID/reference signal selection processmay be periodically or asynchronously changed in response to changingsignal environments, such as where femtocells and associated HeNBs aremoved around in the environment and/or are turned on and off.

In another aspect, multiple eNB's may coordinate the data/controltransmission such that over certain time duration (contiguous ornon-contiguous) or frequency band (contiguous or non-contiguous),certain transmit signals are halted or omitted (also denoted herein as aprotected or restricted interval). For example, in some cases no dataand/or control signals (other than reference signals) are transmitted tofacilitate user equipment (UE) measurement on reference signal. Thiscoordination may be done directly between two or more eNBs/HeNBs viawireless connection and/or may be managed through other connections suchas through a backhaul connection to a core network as is shown in FIGS.1 and 2.

In another aspect, a UE may measure the reference signal strength(difference or ratio) to enable or disable certain receiverfunctionality such as interference cancellation. For example, the UE mayuse the reference signal strength variation over time to determinewhether to enable or disable certain receiver functionality such asinterference cancellation. Metrics used may include RSPR, RSRQ, CQIReport (channel quality indication), RLM (radio link monitoring, basedon SNR of reference signal) or other signal metrics. When referencesignals do not collide from different cells, the reference signalstrength may vary over time due to data and reference signal collision.

Nominally, the UE averages instant channel estimate (channel estimatefrom that symbol and/or adjacent symbols) from different sub frames orOFDM symbols by applying some filtering. Such filtering is traditionallytime-invariant or tunable based on Doppler or signal-to-noise (SNR)information (i.e., fixed filtering). Alternately, in accordance withanother aspect, the UE may use interference information to applydifferent weights on the instant channel estimates over time. This maybe done when there is dynamic scheduling across different cells and eachOFDM or subframe may observe different interference.

Attention is now directed to FIG. 4 which illustrates one embodiment ofa process 400 for interference mitigation by controlling cell IDs. Atstage 410, a wireless network node, which may be an eNB or HeNB, maymonitor transmissions from other wireless network elements, such asother eNBs, HeNBs or UEs. For example, a newly installed or relocatedHeNB may be initialized in proximity to another wireless network, suchas the various networks as shown in FIG. 1. The node may initialize witha predefined cell ID and may then initially listen before startingtransmissions. The node may then detect one or more adjacent cells, suchas other macrocells or femtocells. At stage 420, the node may thendetermine a cell ID or IDs associated with the adjacent cells, and/ormay determine a reference signal pattern associated with the adjacentcell or cells.

Based on this determination, the node may then select a new cell IDand/or reference signal pattern at stage 430 such that the selectedreference signal will mitigate interference with the adjacent cell orcells. This determination may be further based on a power level metricassociated with the adjacent cell or cells, and a threshold may bepredefined such that the cell ID and associated reference signal is onlychanged when the interfering signal exceeds a certain power level orother signal metric. The determination may also be based on the type ofadjacent cell, such as, for example, whether it is a CSG or non-CSGcell. Assuming the cell ID is to be updated, the selected referencesignal may be selected to be orthogonal to one or more receivedreference signals associated with the other cell or cells. The selectedcell ID may be based on available cell ID information that may be storedin the node, such as in a table in memory or other storage medium. Theselected cell ID may also be provided to the node through a backhaulconnection to a core network, such as core network 108 as shown in FIG.1 and/or using an MME or SGW pool as shown in FIG. 2. This process mayinclude consideration at the core network regarding allocation ofreference signals between various known cells in the proximity of thenode. In some embodiments, the node may communicate with nodesassociated with the adjacent cells to select an appropriate cell ID andreference signal. This may be done through a direct wirelesscommunication link and/or via a backhaul connection.

Once an appropriate selected cell ID and associated selected referencesignal has been determined at stage 430, the node may then providetransmissions using the selected reference signal at stage 440. Thepattern associated with the selected reference signal may thenfacilitate interference mitigation by being selected to minimizeinterference or be orthogonal to the reference signal pattern(s) of theadjacent cells, which may facilitate processing in other networkelements, such as UEs, for channel estimation and/or other processing.

In some implementations, the channel may change over time, for example,if new femtocells are added or removed. Consequently, process 400 mayinclude a decision step 450, where the process may be repeatedperiodically or asynchronously depending on changes in the operatingenvironment. For example, certain adjacent cells may create interferencein the evening but not during daytime. In this case, the cell ID of thenode may be changed during times of interference. Other periodic orasychronous re-scheduling of cell ID and associated reference signalsmay also be used. In some environments, femtocells may be added orremoved either periodically or at random. In these cases, two or morenodes associated with the femtocells may communicate, either directly orvia a backhaul network, such as shown in FIGS. 1 and 2, to managereference signal assignments.

As noted previously, transmissions from adjacent cells can affectperformance of network components by creating interference. For example,transmissions from one eNB or HeNB may affect communications betweenanother eNB or HeNB and a UE, or between other network devices. FIG. 1illustrates examples of such interference. In accordance with oneaspect, nodes such as eNBs and HeNBs may communicate with each other tocoordinate transmissions so as to mitigate interference. Thiscommunication may be done directly between nodes and/or may be donethrough a backhaul connection, such as is shown in FIG. 1.

Attention is now directed to FIG. 5 which illustrates one embodiment ofa process 500 for providing such coordination between network nodes. Inparticular, it may be desirable to perform communication between two ormore base stations, such as eNBS and/or HeNBS, to coordinate so that aninterfering node reserves resources (i.e., halts or refrains fromtransmitting certain signals during specified time, frequency ortime/frequency resources) during a protected interval so that othernetwork devices, such as UEs, can perform measurements or other signalprocessing.

Initially, a first network node, such as an eNB or HeNB, may be incommunication with a UE (or other device), such as is shown in FIGS. 1and 2. The UE may be performing measurements such as measuring powerand/or channel characteristics or other signal metrics associated withsignals transmitted by the first network node or other network nodes.Further, signals transmitted from the second network node, which maylikewise be an eNB or HeNB, may be generating interference at the UE. Itmay be desirable to provide a communication channel to the UE from thefirst network node that has reduced interference from the second networknode. To facilitate this, communications of coordination information maybe provided between the first network node and the second network nodeto establish this coordination. The coordination may result in restraintor halting of transmission from the second network node during aspecified time period (also described herein as a restricted timeperiod), wherein signal transmissions from the second (and/or other)nodes are restricted. The restriction may include halting transmissionof vary signal elements, such as by halting transmission of data orcontrol signals.

In particular, in the embodiment shown in FIG. 5, the first network nodemay send a request at stage 520 to nodes associated with the detectedone or more adjacent cells (or to other nodes known to be in proximityto the first network cell). Alternately, or in addition, a communicationlink may have previously been established between the first and secondnetwork nodes, or other network nodes, to facilitate this communication.In some cases, the request to initiate coordination may come initiallyfrom the second network node to the first network node, or from a UE orother network device.

In any case, the request may be received at the second network node(and/or at additional network nodes that may be adjacent and/or causinginterference) at stage 530. The request may include coordinationinformation provided from the first network node, such as cell ID,associated UEs, control information, timing or other control or datainformation to facilitate coordination of transmission. For example, thecoordination information may include information regarding possible timeand/or frequency resources in a resource block during which measurementswish to be made, which may be in a specified protected interval or timeperiod. These may be time and/or frequency contiguous and/ornon-contiguous. The information may identify types of communicationsduring which transmission should be refrained, which may be transmissionof control and/or data information. Reference signals may be sent duringthe specified time interval to facilitate measurements based only on thereference signals during the protected interval.

Subsequent to receipt, the first and second network nodes (and/or anyother network nodes in communication) may further exchange informationregarding particular resources that may be controlled so as to mitigateinterference. This may involve, for example, negotiation between thenetwork nodes to determine particular resource elements or otherinformation to be coordinated. This may also include informationassociated with determinations made by agreement or by the secondnetwork node regarding transmission controls, such as, for example, timeand/or frequency resources on which communications will be halted fromthe second network node to facilitate measurement. As noted previously,this may include certain restricted or protected time periods,frequencies, or both, which may be contiguous or non-contiguous. Duringthese controlled time intervals, transmission of data and/or controlinformation may be halted.

At stage 540, the second network node will then control transmissions tomitigate interference based on the transmission coordination informationduring a protected interval. This may be done to allow the UE to makemeasurements with respect to the first network node in the absence oftransmissions from the second network node and/or to make othermeasurements or perform other signal processing at stage 570.Information regarding the controlled transmissions may be provided fromthe first network node to the UE, which may then use this information toperform targeted measurements and/or perform other processing during theprotected interval. In some case, the UE may operate independent ofknowledge of the controlled transmissions, and may provide data, such aschannel measurements, power levels, or other information, to the firstnetwork node at stage 570, which may then share this information withother network nodes, such as the second network node, and/or theinformation may be used to control transmissions from the second networknode and/or other network nodes. In some embodiments, this informationmay be used to determine a different reference signal pattern to be usedby the first or second wireless network nodes, such as was describedpreviously herein with respect to FIG. 4. The node may resume normaloperation at stage 550. In some cases, process 500 may be repeatedlyperiodically or asynchronously to facilitate additional measurements andadjustments.

Measured information may further be used by the UE to control deviceoperation. For example, a UE may perform measurements and/or othersignal processing of signals received from the first wireless networknode (and/or other wireless network nodes besides the second wirelessnetwork node) during the protected interval period at stage 580. Thesemay include various metrics, such as RSRP, RSRQ, CQI information, radiolink monitoring (RLM), radio link failure monitoring (RLFM) and/or othersignal power metrics.

The UE may then use the information measured during the protectedinterval to adjust receiver functionality and/or disable or enablecertain receiver functions at stage 590. For example, the informationobtained during the controlled transmission period may be used by thereceiver to turn on or off interference cancellation functionality inthe UE. If the interference level associated with the second wirelessnetwork is high, interference cancellation may be turned off at the UEto save battery power (assuming interference cancellation would not beeffective at high interference levels). Conversely, if interference fromthe second wireless network node is low or intermittent, interferencecancellation may be enabled. Other receiver functionality, such as maybe associated with the level of an interfering signal, maycorrespondingly be controlled in response to measurements made duringthe controlled transmission period.

In addition, a UE may measure reference signal strength over time andmay adjust receiver functionality based on variation over time. Forexample, when reference signals from other cells collide over time thereceived signals may vary. Accordingly, metrics such as RSRP, RSPQ, CQI,radio link monitoring (RLM) measurements, radio link failure monitor(RLFM) measurements, or other signal power metrics may be used to enableor disable receiver functionality over time. This may be based on, forexample, a threshold level of interference, above or below whichfunctionality may be changed. In an exemplary embodiment, a receiversub-system in a UE (or other network device) includes an interferencecancellation (IC) module, which consumes power when on. If thedetermined interference level changes, the functionality of the ICmodule may be switched on or off, depending on whether interferencecancellelation would be appropriate in the current environment.

FIG. 6 illustrates an embodiment of a process 600 for performing dynamicfunctionality control. At stage 610 a receiver, such as a UE, maymonitor signals received from multiple cells, with corresponding firstand second cell reference signals. An interference level may begenerated at stage 620 based on this monitoring, which may be, forexample, a power level or signal strength parameter such as RSRP, RSRQ,RLM, RLFM, CQI, and the like, or another signal metric. At stage 630,the interference level may be compared with one or more metrics, such asa threshold value or range of values, a moving average value, or othervalue or parameter associated with a receiver functionality. If theinterference level exceeds the threshold, a receiver functionality maybe controlled. For example, inteference cancellation may be enabled ordisabled in response to a dynamic interference level so as to managebattery consumption.

It is noted that the terms “first wireless network node” and “secondwireless network node” are used above for purposes of explanation, andthat various specific nodes in particular systems may correspond to therepresentative first and second wireless network nodes described herein.

As noted previously, receiver functionality such as is included in a UEperforms instant channel estimates (i.e., channel estimates from aparticular symbol or a symbol and adjacent symbols), which may be basedon received reference signals. Traditionally, these instant channelestimates are averaged over multiple subframes or OFDM symbols, each ofwhich have a reference signal. This is often done by using a filter suchas a FIR filter, such as a 3 tap filter which may average over 2milliseconds. The filtering is normally time-invariant or tunable basedonly on Doppler or signal to noise ratio (SNR) information.

In another aspect, different filtering for channel estimation may beapplied over different subframes, which may be based on instant channelestimates associated with the subframes. In particular, interferencelevels may vary between subframes based on the particularcharacteristics of signals received during the subframes. For example,subframes may be subject to significant interference such as fromadjacent networks, whereas other subframes may be subject to lessinterference. To address this, a UE (or other node implementing receiverfunctionality, may perform instant channel estimates and collectinterference information, which may be time varying over intervals ofsub-frames. Based on this information, the UE may then generatedifferent weightings for the channel estimates and/or may applydifferent filtering based on the instant estimates rather than anaverage taken over multiple subframes.

FIG. 7 illustrates a process 700 for adjusting a receiver to account forinterference. The receiver may monitor interference levels associatedwith multiple adjacent cells or devices at stage 710. In particular,this may include interference from multiple reference signals fromdifferent nodes, which may increase or decrease at the level of timeresolution of sub-frames. A time variation in the interference level,corresponding to subframe levels may then be determined. For example,each OFDM symbol or subframe may see different interference, which maybe the case when there is dynamic scheduling across different cells.Based on detection of the interference, channel estimates may beweighted accordingly so as to allow adjustment at the sub-frame level orbelow at stage 730. A filter response may be adjusted based on theweighting or on the instant channel estimate.

Attention is now directed to FIG. 8, which illustrates a wirelesscommunications methodology which may be implemented on a system such asis shown in FIG. 1. While, for purposes of simplicity of explanation,the methodology (and other methodologies described herein) are shown anddescribed as a series of acts, it is to be understood and appreciatedthat the methodology is not limited by the order of acts, as some actsmay, in accordance with one or more aspects, occur in different ordersand/or concurrently with other acts from that shown and describedherein. In some implementations some acts may be omitted, whereas inother implementations some acts may be added. For example, those skilledin the art will understand and appreciate that a methodology couldalternatively be represented as a series of interrelated states orevents, such as in a state diagram. Moreover, not all illustrated actsmay be utilized to implement a methodology in accordance with theclaimed subject matter.

At stage 810, reference mapping is employed. If a base station such asan eNB (or HeNB) locates a strong cell, the eNB can select a cell IDsuch that reference signal mapping are orthogonal to this strong cell,where a reference signal occupies different frequency resources used bythis cell. The eNB may decide to apply the strategy above based on thetype of a cell which causes strong interference, e.g., based on whetherthe cell is a closed subscriber group (CSG) cell or non-CSG cell.

At stage 820, multiple eNB's (and/or HeNBs) may coordinate data/controltransmission such that over certain time periods (contiguous ornon-contiguous) or frequency bands (contiguous or non-contiguous), nodata and or control signal (other a reference signal) are transmitted,so as to facilitate user equipment (UE) measurements on the referencesignal(s).

At stage 830, the UE may measure the reference signal strength(difference or ratio) to enable or disable certain receiverfunctionality such as interference cancellation. In another aspect, theUE may use reference signal strength variations over time to determinewhether to enable or disable certain receiver functionality, such asinterference cancellation. When reference signals do not collide fromdifferent cells, the reference signal strength may vary over time due todata and reference signal collision.

At stage 840, the UE may generate instant channel estimates (channelestimates from the corresponding OFDM symbol and/or adjacent symbols).The UE may use associated interference information to apply differentweights on the instant channel estimates over time. This may be donewhen there is dynamic scheduling across different cells and each OFDM orsubframe may observe different interference. By using this approach,receiver performance may be enhanced over traditional methods that useaveraging of channel estimates.

Attention is now directed to FIG. 9, which illustrates a block diagramof an embodiment of base station 910 (i.e., an eNB or HeNB) and aterminal 950 (i.e., a terminal, AT or UE) in an example LTE MIMOcommunication system 900. These systems may correspond to those shown inFIGS. 1-3, and may be configured to implement the processes illustratedpreviously herein in FIGS. 4-7.

Various functions may be performed in the processors and memories asshown in base station 910 (and/or in other components not shown), suchas selection of cell ID based on adjacent node information, outputtransmit control to provide protected intervals based on coordinationinformation received from other base stations, as well as otherfunctions as described previously herein. UE 950 may include one or moremodules to receive signals from base station 910 to determine channelcharacteristics such as channel estimates, demodulate received data andgenerate spatial information, determine power level information, and/orother information associated with base station 910.

In one embodiment, base station 910 may adjust output in response toinformation received from UE 950 or from backhaul signaling from anotherbase station (not shown in FIG. 9) as described previously herein. Thismay be done in one or more components (or other components not shown) ofbase station 910, such as processors 914, 930 and memory 932. Basestation 910 may also include a transmit module including one or morecomponents (or other components not shown) of HeNB 910, such as transmitmodules 924. Base station 910 may include an interference cancellationmodule including one or more components (or other components not shown),such as processors 930, 942, demodulator module 940, and memory 932 toprovide interference cancellation functionality. Base station 910 mayinclude a coordination module including one or more components (or othercomponents not shown), such as processors 930, 914 and memory 932 toreceive coordination information from other network devices and managethe transmitter module based on the coordination information. Basestation 910 may also include a control module for controlling receiverfunctionality, such as turning on or off other functional modules suchas the interference cancellation module. Base station 910 may include anetwork connection module 990 to provide networking with other systems,such as backhaul systems in the core network or other components asshown in FIGS. 1 and 2.

Likewise, UE 950 may include a receive module including one or morecomponents of UE 950 (or other components not shown), such as receivers954. UE 950 may also include a signal information module including oneor more components (or other components not shown) of UE 950, such asprocessors 960 and 970, and memory 972. In one embodiment, one or moresignals received at UE 950 are processed to estimate channelcharacteristics, power information, spatial information and/or otherinformation regarding corresponding HeNBs, such as base station 910.Memories 932 and 972 may be used to store computer code for execution onone or more processors, such as processors 960, 970 and 938, toimplement processes associated with channel measurement and information,power level and/or spatial information determination, cell ID selection,inter-cell coordination, interference cancellation control, as well asother functions as are described herein.

In operation, at the base station 910, traffic data for a number of datastreams may be provided from a data source 912 to a transmit (TX) dataprocessor 914, where it may be processed and transmitted to one or moreUEs 950. The transmitted data may be controlled as described previouslyherein so as to mitigate interference or perform signal measurements atone or more UEs 950.

In one aspect, each data stream is processed and transmitted over arespective transmitter sub-system (shown as transmitters 924 ₁-924_(Nt)) of base station 910. TX data processor 914 receives, formats,codes, and interleaves the traffic data for each data stream based on aparticular coding scheme selected for that data stream so as to providecoded data. In particular, base station 910 may be configured todetermine a particular reference signal and reference signal pattern andprovide a transmit signal including the reference signal and/orbeamforming information in the selected pattern.

The coded data for each data stream may be multiplexed with pilot datausing OFDM techniques. The pilot data is typically a known data patternthat is processed in a known manner and may be used at the receiversystem to estimate the channel response. For example, the pilot data maycomprise a reference signal. Pilot data may be provided to TX dataprocessor 914 as shown in FIG. 9 and multiplexed with the coded data.The multiplexed pilot and coded data for each data stream may then bemodulated (i.e., symbol mapped) based on a particular modulation scheme(e.g., BPSK, QSPK, M-PSK, M-QAM, etc.) selected for that data stream soas to provide modulation symbols, and the data and pilot may bemodulated using different modulation schemes. The data rate, coding, andmodulation for each data stream may be determined by instructionsperformed by processor 930 based on instructions stored in memory 932,or in other memory or instruction storage media of UE 950 (not shown).

The modulation symbols for all data streams may then be provided to a TXMIMO processor 920, which may further process the modulation symbols(e.g., for OFDM implementation). TX MIMO processor 920 may then provideNt modulation symbol streams to N_(t) transmitters (TMTR) 922 ₁ through922 _(Nt). The various symbols may be mapped to associated RBs fortransmission.

TX MIMO processor 920 may apply beamforming weights to the symbols ofthe data streams and corresponding to the one or more antennas fromwhich the symbol is being transmitted. This may be done by usinginformation such as channel estimation information provided by or inconjunction with the reference signals and/or spatial informationprovided from a network node such as a UE. For example, a beamB=transpose([b1 b2 . . . b_(Nt)]) composes of a set of weightscorresponding to each transmit antenna. Transmitting along a beamcorresponds to transmitting a modulation symbol x along all antennasscaled by the beam weight for that antenna; that is, on antenna t thetransmitted signal is bt*x. When multiple beams are transmitted, thetransmitted signal on one antenna is the sum of the signalscorresponding to different beams. This can be expressed mathematicallyas B1x1+B2x2+BN_(S)×N_(S), where N_(S) beams are transmitted and xi isthe modulation symbol sent using beam Bi. In various implementationsbeams could be selected in a number of ways. For example, beams could beselected based on channel feedback from a UE, channel knowledgeavailable at the eNB, or based on information provided from a UE tofacilitate interference mitigation, such as with an adjacent macrocell.

Each transmitter sub-system 922 ₁ through 922 _(Nt) receives andprocesses a respective symbol stream to provide one or more analogsignals, and further conditions (e.g., amplifies, filters, andupconverts) the analog signals to provide a modulated signal suitablefor transmission over the MIMO channel. N_(t) modulated signals fromtransmitters 922 ₁ through 922 _(Nt) are then transmitted from N_(t)antennas 924 ₁ through 924 _(Nt), respectively.

At UE 950, the transmitted modulated signals are received by N_(r)antennas 952 ₁ through 952 _(Nr) and the received signal from eachantenna 952 is provided to a respective receiver (RCVR) 954 ₁ through952 _(Nr). Each receiver 954 conditions (e.g., filters, amplifies anddownconverts) a respective received signal, digitizes the conditionedsignal to provide samples, and further processes the samples to providea corresponding “received” symbol stream.

An RX data processor 960 then receives and processes the N_(r) receivedsymbol streams from N_(r) receivers 954 ₁ through 952 _(Nr) based on aparticular receiver processing technique so as to provide N_(S)“detected” symbol streams so at to provide estimates of the N_(S)transmitted symbol streams. The RX data processor 960 then demodulates,deinterleaves, and decodes each detected symbol stream to recover thetraffic data for the data stream. The processing by RX data processor960 is typically complementary to that performed by TX MIMO processor920 and TX data processor 914 in base station 910.

A processor 970 may periodically determine a precoding matrix for use asis described further below. Processor 970 may then formulate a reverselink message that may comprise a matrix index portion and a rank valueportion. In various aspects, the reverse link message may comprisevarious types of information regarding the communication link and/or thereceived data stream. The reverse link message may then be processed bya TX data processor 938, which may also receive traffic data for anumber of data streams from a data source 936 which may then bemodulated by a modulator 980, conditioned by transmitters 954 ₁ through954 _(Nr), and transmitted back to base station 910. Informationtransmitted back to base station 910 may include power level and/orspatial information for providing beamforming to mitigate interferencefrom base station 910.

At base station 910, the modulated signals from UE 950 are received byantennas 924, conditioned by receivers 922, demodulated by a demodulator940, and processed by a RX data processor 942 to extract the messagetransmitted by UE 950. Processor 930 then determines which pre-codingmatrix to use for determining beamforming weights, and then processesthe extracted message.

In some configurations, the apparatus for wireless communicationincludes means for performing various functions as described herein. Inone aspect, the aforementioned means may be a processor or processorsand associated memory in which embodiments reside, such as are shown inFIG. 9, and which are configured to perform the functions recited by theaforementioned means. The may be, for example, modules or apparatusresiding in UEs, HeNBs and/or eNBs such as are shown in FIGS. 1-3 andFIG. 9. In another aspect, the aforementioned means may be a module orany apparatus configured to perform the functions recited by theaforementioned means.

In one or more exemplary embodiments, the functions, methods andprocesses described may be implemented in hardware, software, firmware,or any combination thereof. If implemented in software, the functionsmay be stored on or encoded as one or more instructions or code on acomputer-readable medium. Computer-readable media includes computerstorage media. Storage media may be any available media that can beaccessed by a computer. By way of example, and not limitation, suchcomputer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code in the form of instructions or data structures and that canbe accessed by a computer. Disk and disc, as used herein, includescompact disc (CD), laser disc, optical disc, digital versatile disc(DVD), floppy disk and blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media.

It is understood that the specific order or hierarchy of steps or stagesin the processes and methods disclosed are examples of exemplaryapproaches. Based upon design preferences, it is understood that thespecific order or hierarchy of steps in the processes may be rearrangedwhile remaining within the scope of the present disclosure. Theaccompanying method claims present elements of the various steps in asample order, and are not meant to be limited to the specific order orhierarchy presented.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps or stages of a method, process or algorithm described inconnection with the embodiments disclosed herein may be embodieddirectly in hardware, in a software module executed by a processor, orin a combination of the two. A software module may reside in RAM memory,flash memory, ROM memory, EPROM memory, EEPROM memory, registers, harddisk, a removable disk, a CD-ROM, or any other form of storage mediumknown in the art. An exemplary storage medium is coupled to theprocessor such that the processor can read information from, and writeinformation to, the storage medium. In the alternative, the storagemedium may be integral to the processor. The processor and the storagemedium may reside in an ASIC. The ASIC may reside in a user terminal. Inthe alternative, the processor and the storage medium may reside asdiscrete components in a user terminal.

The claims are not intended to be limited to the aspects shown herein,but is to be accorded the full scope consistent with the language of theclaims, wherein reference to an element in the singular is not intendedto mean “one and only one” unless specifically so stated, but rather“one or more.” Unless specifically stated otherwise, the term “some”refers to one or more. A phrase referring to “at least one of” a list ofitems refers to any combination of those items, including singlemembers. As an example, “at least one of: a, b, or c” is intended tocover: a; b; c; a and b; a and c; b and c; and a, b and c.

The previous description of the disclosed aspects is provided to enableany person skilled in the art to make or use the present disclosure.Various modifications to these aspects will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other aspects without departing from the spirit or scope ofthe disclosure. Thus, the disclosure is not intended to be limited tothe aspects shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein. Itis intended that the following claims and their equivalents define thescope of the disclosure.

I claim:
 1. A method, comprising: determining a time variation in ameasurable parameter of one or more reference signals; and modifying afunctionality of a receiver based upon the time variation.
 2. The methodof claim 1, wherein the functionality of the receiver comprisesinterference cancellation.
 3. The method of claim 1, wherein themodifying comprises disabling the functionality of the receiver.
 4. Themethod of claim 1, wherein the modifying comprises enabling thefunctionality of the receiver.
 5. The method of claim 1, wherein themeasurable parameter is selected from the set consisting of RSRP, RLF,RSRQ and CQI.
 6. A computer program product comprising a computerreadable medium including codes for causing a computer to: determine atime variation in a measurable parameter of one or more referencesignals; and modify a functionality of a receiver based upon the timevariation.
 7. The computer program product of claim 6, wherein thefunctionality of the receiver comprises interference cancellation. 8.The computer program product of claim 6, wherein the modifying comprisesdisabling the functionality of the receiver.
 9. The computer programproduct of claim 6, wherein the modifying comprises enabling thefunctionality of the receiver.
 10. The computer program product of claim6, wherein the measurable parameter is selected from the set consistingof RSRP, RLF, RSRQ and CQI.
 11. An apparatus for use in a communicationsystem, comprising: a receiver module configured to determine a timevariation in a measurable parameter of one or more reference signals;and a control module configured to modify a functionality of a receiverbased upon the time variation.
 12. The apparatus of claim 11, whereinthe functionality of the receiver comprises interference cancellation.13. The apparatus of claim 11, wherein the modifying comprises disablingthe functionality of the receiver.
 14. The apparatus of claim 11,wherein the modifying comprises enabling the functionality of thereceiver.
 15. The apparatus of claim 11, wherein the measurableparameter is selected from the set consisting of RSRP, RLF, RSRQ andCQI.
 16. An apparatus for use in a communication system, comprising:means for determining a time variation in a measurable parameter of oneor more reference signals; and means for modifying a functionality of areceiver based upon the time variation.
 17. The apparatus of claim 16,wherein the functionality of the receiver comprises interferencecancellation.
 18. The apparatus of claim 16, wherein the means formodifying comprises disabling the functionality of the receiver.
 19. Theapparatus of claim 16, wherein the means for modifying comprisesenabling the functionality of the receiver.
 20. The apparatus of claim16, wherein the measurable parameter is selected from the set consistingof RSRP, RLF, RSRQ and CQI.